When a semiconductor device and a flat panel display are manufactured, a process of cleaning substrates used for manufacturing thereof is appropriately performed. In the cleaning process, a cleaning liquid is discharged to the substrate and residues adsorbed on the substrate are cleaned by the cleaning liquid. There are many cases where the cleaning liquid is heated in order to improve the cleaning effect and a heating unit for heating the liquid is used for the heating. See, for example, Japanese Patent Application Laid-Open No. 2003-90614.
A liquid heating device disclosed in Japanese Patent Application Laid-Open No. 2003-90614 includes a lamp heater capable of radiationally heating a liquid, such as a mercury lamp or a halogen lamp. The liquid heating device also includes a cylindrical liquid tank made of quartz having light transmittance and chemical resistance and having a hollow portion where the lamp heater is placed. In the liquid tank, an inlet and an outlet are provided for the liquid, and the liquid that flows into the liquid tank from the inlet is heated to a predetermined temperature by the lamp heater placed in the hollow portion and discharged from the outlet to be supplied to a liquid processing apparatus.